A drill stem test may be considered to be a temporary completion of an earth formation that has been intersected by a well bore. A packer is run into the well on a pipe string and is set to isolate the interval of the well bore to be tested, and then a test valve is opened to permit fluids in the formation to flow into the borehole and up into the pipe string to obtain an indication of the commercial potential of the well. Pressure data is recorded with the test interval open and then shut in, from which many useful parameters such as permeability and initial reservoir pressure can be determined. It also is desirable to collect an actual sample of the fluids for subsequent laboratory analysis.
A sampler that has been used for many years with great success is disclosed in Nutter U.S. Pat. No. 3,308,887, assigned to the assignee of this invention. As shown in FIG. 3B of that patent, the flow of formation fluid is routed through an annular chamber having sleeve valves at each end that can be simultaneously opened or closed. When the valves finally are closed at the end of the test, a flowing sample of the fluid being produced is entrapped at formation conditions of temperature and pressure. However, the testing apparatus shown in the Nutter patent has a barrier that blocks vertical access through the tool and which must be removed before other equipment such as a pressure recorder or a perforator can be run into the well.
A sampler valve that uses a pair of vertically spaced ball valves to simultaneously open and close the respective ends of a sample chamber is shown in U.S. Pat. No. 4,063,593. The device shown in the '593 patent, while being full-bore, is considered to be unduly complicated and thus subject to malfunction in use in the well.
It is the general object of the present invention to provide a new and improved full-bore sampler valve for trapping the last flowing sample of formation fluids that are produced during a drill stem test.
Another object of the present invention is to provide a new and improved full-bore sampler apparatus that can be closed responsive to a specific annulus pressure signal to trap a sample and to also function as a safety valve when closed to shut in the formation being tested.